A Wire Bonder is a machine with which wire connections are made to semiconductor chips after they have been mounted on a substrate. The Wire Bonder has a capillary that is clamped to the tip of a horn. The capillary serves to secure the wire to a connection point on the semiconductor chip and to a connection point on the substrate as well as to guide the wire between the two connection points. On making the wire connection between the connection point on the semiconductor chip and the connection point on the substrate, the end of the wire protruding from the capillary is first melted into a ball. Afterwards, the wire ball is secured to the connection point on the semiconductor chip by means of pressure and ultrasonics. In doing so, ultrasound is applied to the horn from an ultrasonic transducer. This process is known as ball bonding. The wire is then pulled through to the required length, formed into a wire loop and welded to the connection point on the substrate. This last process is known as wedge bonding. After securing the wire to the connection point on the substrate, the wire is torn off and the next bond cycle can begin.
Ball bonding as well as wedge bonding are influenced by various factors. In order to achieve bond connections of a predetermined quality, the adequate values of several physical and/or technical parameters must be determined for a particular process. Examples of such parameters are:    the bond force, that is the normal force which the capillary exerts on the ball bond or the connection point of the semiconductor chip during the bonding process,    a parameter, designated herein as ultrasonic variable P, which controls the application of ultrasound to the ultrasonic transducer. The ultrasonic variable is, for example, the amplitude of the alternating current which flows through the ultrasonic transducer of the horn or the amplitude of the alternating voltage which is applied to the ultrasonic transducer, or the power, or another variable,    a time duration, designated herein as ultrasonic time T, which indicates the length of time that the ultrasonic variable P is applied to the ultrasonic transducer,    the impact velocity of the capillary on the connection point,    a binary parameter that indicates whether the ultrasonic variable is already applied to the ultrasonic transducer before the capillary impacts on the connection point.
Today, in order to characterise the bond quality in the sense of a quality control as well as to determine the optimum bond parameters, two methods are primarily used namely    a) a so-called Pull Test, with which the force is measured at which the bond tears away from the semiconductor chip or substrate when the bond is pulled in, vertical direction in relation to the surface of the semiconductor chip or substrate, and    b) a so-called Shear Test, with which the force is measured at which the bond tears away from the semiconductor chip or substrate when the bond is pushed away parallel to the surface of the semiconductor chip or substrate by means of a tool.
These tests are normally carried out with equipment specially developed for this application. However, from the patent U.S. Pat. No. 5,894,981, a Wire Bonder is known which is set up to carry out a Pull Test. This Wire Bonder concerns a specific method for forming the wire loops with which the wire is not fed by a capillary. With the Pull Test, after forming the wedge bond, the wire is pulled away in a direction running vertically to the surface. The disadvantage with this test is that the check takes place before the bond cycle is completed as the wedge bond is still connected to the wire feed device.
From the patent U.S. Pat. No. 5,591,920, a Wire Bonder is known which is set up to carry out a Pull Test with which the maximum current is measured which flows through a motor that raises and lowers the capillary. This test can be carried out for Ball Bonds as well as for Wedge Bonds. When this Pull Test is carried out for a Wedge Bond, then an important disadvantage exists in that, on testing, load is not put on the wedge as with the established Pull Test, but on the piece of wire which is to be torn off in the last stage of the bond cycle, the so-called tail.